Mutations of TNFRSF13B in 50 of 564 index patients with antibody deficiency. Distribution of the observed TNFRSF13B mutations across the TNFRSF13B/TACI protein. Each symbol represents one patient. ● indicates patients with homozygous TNFRSF13B mutations. ○ represents patients with heterozygous TNFRSF13B mutations. designates a patient with a double mutation on one allele of TNFRSF13B. Compound heterozygous mutated TACI-deficient patients are labeled as indicated in the figure. CRD indicates cysteine-rich domain; stalk, stalk region; and TM, transmembrane domain.